Rate coefficients for photoinitiated NO2 unimolecular decomposition:: energy dependence in the threshold regime

Rate coefficients k(E) for photoinitiated NO2 unimolecular decomposition have been obtained by recording the product NO laser-induced fluorescence signal intensity versus the delay between the pump and probe pulses. A 10 ps pump-probe cross-correlation temporal width provides a useful compromise between time and frequency resolution (3 cm(-1)). k(E) increases rapidly: from similar to 2 x 10(10) to greater than or equal to 1.3 x 10(11) s(-1) within 25 cm(-1) of reaction threshold. In this regime, long-range interfragment interactions play an important role. A high level of theory will be needed to reconcile these results. (C) 2002 Published by Elsevier Science B.V.